This invention relates to high temperature seal members and, more particularly, to a high temperature seal material especially useful in the high temperature portions of gas turbine engines and having an improved combination of oxidation and gas erosion resistance, reduced thermal conductivity and low flow stress rather than abradability.
An important factor in the evolution of gas turbine engines has been the development of new turbine materials technology. The desire for increased turbine inlet temperatures has been persistent, resulting in the development of improved turbine blade and vane materials to withstand the more difficult conditions. Concurrently, improvements in turbine shroud materials are required not only to withstand the higher temperatures, but also to resist the more difficult oxidation and gas erosion conditions while assisting and improving the efficiency of the turbine.
Early forms of turbine shrouds were relatively simple metal rings that defined the outer gas envelope. Improved forms included open-face honeycomb, transpiration cooled materials as a result of air permeability through the material, and shrouds filled with various types of abradable, friable materials. One such shroud currently operating in commercial gas turbine engines is filled with a material sometimes referred to as Bradelloy material and is described in U.S. Pat. No. 3,342,563 -- Butts, issued Sept. 19, 1967. This material has resulted in a reliable turbine shroud structure for current operating temperatures. However, it has been recognized that the higher temperatures and more difficult operating conditions found in advanced gas turbine engines will require an improved high temperature shroud member which is more oxidation and erosion resistant, and is substantially non-friable at intended operating temperatures. Thus it can flow or smear at elevated temperatures at the interface with a rubbing element such as a blade tip, to provide a smooth, highly finished, aerodynamically desirable surface.